In motor control devices for driving machine tools, industrial machines, robots and the like, there is a known method for preventing a motor from operating in case of emergency shut-down or raising an alarm, by which an electromagnetic connector provided in an input power line is turned off to disconnect the motor control device from a power source so that power supply from the power source is stopped (for example, Japanese Patent No. 3506590 (JP 3506590 B)).
According to this conventional method, excessive current passing through the electromagnetic connector can possibly weld a contact and disable the electromagnetic connector from disconnecting. Therefore, generally a method in which the electromagnetic connector is turned on and off in a state of stopping a machine and consuming no energy, and an auxiliary contact of the electromagnetic connector is monitored at this time in order to check the presence or absence of welding of the electromagnetic connector is used (for example, Japanese Patent Laid-Open Publication No. 2007-181885 (JP 2007-181885 A)).
However, this conventional art requires providing the electromagnetic connector having the auxiliary contact, and also an additional circuit for monitoring the auxiliary contact in a motor drive or the outside thereof, resulting in an increase in costs.
An object of the present invention is to provide a motor drive that can detect the presence or absence of welding of an electromagnetic connector without an increase in costs, by utilizing a DC link voltage detection unit or a current detection unit, without requiring the provision of the auxiliary contact of the electromagnetic connector and the additional circuit.